People in Yangzhou, Jiangsu province take part in the traditional activity of wearing willow branch hats on April 4, the day of clear and bright. Meng Delong / for China Daily

Business opportunities

The themes of the 24 solar periods have also become a marketing tool for department stores and online retailers, who try to recommend tailor-made products to potential customers.

"Western festivals, such as Valentine's Day and Thanksgiving, are important times to boost consumption. Similarly, the solar terms are helpful in selling seasonal products," said Luo Shujuan, a 26-year-old beauty consultant at a department store on Nanjing Road, one of the busiest streets in downtown Shanghai.

"The change in solar periods usually results in changes in demand for skincare products. If you have an insight into these delicate shifts from days that are humid but not too hot, to those that are scorching, dry-and-cool to freezing, it is much easier to understand the products most helpful to consumers," said Luo.

Like many of her peers, Luo comes from a family that relied on farming as its major source of income. The 24-solar-term cycle feels "embedded in my mind", said Luo.

"It's traditional wisdom, based on long-time observations. It helps people to understand the best times for sowing various vegetables and grains, irrigating the land, and harvesting the produce. I use the same principles to provide skincare advice to customers, because the fundamental idea behind it is to do the right thing at the right time," said Luo.